The present invention relates to the separation of aromatic compounds from slack wax, such as that obtained in urea and solvent dewaxing processes, using a macroporous metal ion loaded cation exchange resin.
There has been an increasing demand for n-paraffins for use in the petrochemical industry, e.g., for the production of bio-degradable detergents, long-chain alcohols, plasticizers etc. Other applications of n-paraffins include the production of proteins which has been carried out on a large scale in the past few years. The two principal steps of all petro-protein production processes consist in the fermentation and subsequent recovery of the protein-containing cells. Processes using methane and other gaseous hydrocarbons consist of these two stages, while in processes using liquid hydrocarbons as the nutrient solution further process steps have to be added for the production of pure n-paraffin, such as an additional purification step as the last step of the process, particularly when gas oil or other crude oil fractions are employed as the feed. The degree of purity of the charge is of vital importance when considering the economy of such processes.
Petroprotein manufacturers are not alone in setting high standards for the purity of the n-paraffin charge materials; other manufacturers, too, require greater purity of the n-paraffins, and food regulations insist on the removal of impurities, e.g., removal of aromatic compounds in case the paraffins are processed in the food industry for use in packaging material or coating of milk containers or for other applications, e.g. chewing gum, or for use as petroleum jelly according to DAB VII (Deutsches Aerztebuch VII -- German Manual for Pharmacists and Pharmaceutical Industry) in the pharmaceutical and/or cosmetic industries. Thus, the manufacturers of paraffins were required to raise the degree of purity of their products.
Presently large amounts of normal hydrocarbons are obtained via urea adducts according to the Edeleanu process. Initially, this process was used for dewaxing crude oil products, gas oil and spindle oil for producing low-pour oils; later on, it was further developed and modified to permit the production of pure normal hydrocarbons. In another industrial process molecular sieves are employed for the recovery of pure n-paraffins. The commercial molecular sieve processes may be divided into two groups, namely: gas phase and liquid phase processes. These processes include three process steps: adsorption, freeing the molecular sieve from adherent hydrocarbons which are not of the n-paraffin type subsequent to the adsorption step, and desorption. The desorption process is slower than the adsorption process and, therefore, should be as short as possible with respect to the efficiency of the unit. A variety of desorption techniques is known for use in units being operated with molecular sieves.
The paraffins contained in the gas oil and lubricating oil fractions are separated therefrom in order to improve the low-temperature characteristics of the products produced from said fractions. The fractions are dewaxed mainly by precipitating the paraffins at low temperatures with the aid of solvents such as benzene plus methyl ethyl ketone, propane, and dichloroethane plus dichloromethane. The separated paraffin still contains large amounts of oil and is called slack wax. These slack waxes contain between 3 and 30 percent of oily components, the oil being removed by sweating or by solvent de-oiling. Finally, the slack waxes are refined by treating them with bleaching earth; a more effective, though costly, procedure is, however, to pretreat them with concentrated or fuming sulfuric acid and then with bleaching earth.
German Offenlegungsschrift No. P 22 52 305.3 discloses a process for the production of n-paraffins useful as starting materials for petroleum fermentation products for use in foodstuff on animal feed wherein the carcinogenic aromatic hydrocarbons have been removed and wherein the n-paraffins containing less than 0.1 ppm of benzo (.alpha.) pyrene are subjected to an adsorption treatment. Alumina having a particle size of from 8 to 100 mesh, a surface area above 100 square meters per gram and a SiO.sub.2 content of below 15 weight percent is used as the adsorbent. The adsorption step is followed by the desorption step in which the hydrocarbons retained on the adsorbent are desorbed. The method of regeneration through solvent treatment, steam treatment and drying at temperatures of from 220.degree. to 250.degree.C, which has been proposed in order to permit repeated use of the adsorbing media, involves heavy stress on the adsorption media as far as their structure is concerned, resulting in a shorter lifetime of these media.
U.S. Pat. No. 3,409,691 proposes to separate polar organic materials from less polar materials by sorption with a solid sorbent, using as the sorbent a dry macroporous cation exchange resin or a metal salt thereof having a specific surface area of at least 20 square meters per gram. As polar organic materials which are separated from an aliphatic hydrocarbon, the U.S. patent specification mentions alcohols, aldehydes, ketones, ethers, mercaptans, chlorinated hydrocarbons, olefins, and aromatic hydrocarbons. The patent specification does not teach, however, whether and how the purification of slack waxes existing in semi-solid to solid form at normal temperature can be performed. Neither does this patent disclose a technique whereby the process may be performed on a continuous basis acceptable for commercial use.
When n-paraffins are purified according to conventional methods, there occur more or less large amounts of spent bleaching earth and acid resins the disposal of which only raises costs, since one cannot dispose of these materials at the usual waste pits for reasons of protection of environment. If the n-paraffins are purified using silica gel or alumina, the loading capacity is relatively limited and the desorption step and subsequent re-use of the regenerated adsorbents are possible only at considerable costs. Finally, cation exchange resin was found to be unsuitable when used for removing concomitant impurities, especially traces of aromatic substances, from the n-paraffin mixtures in the batch procedure described in the above-mentioned patent specification.